Due in part to the complex life-cycle of freshwater mussels usually involving a parasitic stage on fish host and to unknown environmental or habitat requirements, many freshwater mussel species have been recognized as declining in numbers and/or extirpated from historical habitats. Therefore, approximately 15 percent of all animal species recognized by law as endangered include various species of freshwater mussels.
Initiation of research leading to the present invention was for the specific purpose of developing a culture medium for use in conservation of endangered freshwater mussels. However, the instant invention is highly relevant to management and conservation of commercial freshwater mussel species, shells of which were used historically for making buttons and presently for making nuclei for cultured pearls.
Historically, Ellis et al (1926, Science, Vol. 54, No. 1667, pages 579-580; and 1929 Trans. Amer. Fish Soc., Vol. 59, pages 217-223) claimed to have obtained transformation of freshwater mussel glochidia to young adult mussels; however, if they did, neither the process nor the composition of matter was ever published to the extent their work could be reproduced. The research described herein utilized processes and composition of matter unavailable during Ellis's research and certainly during the period of their purported successes.
Since each gravid mussel may have tens of thousands of glochidia, it is obvious that if they could be cultured artificially there would be significant commercial and conservation potential. There appear to be no historical data base other than the claims of Ellis et al, supra, relevant to the present invention.
Since glochidia parasitizing fish are known to obtain some essential stimulus and nourishment from the fish blood plasma in order to transform from the larval or glochidial stage to the young adult stage, it was thought that the best chance of artificial habitat culture was to simulate this complex chemical environment in the artificial habitat. Thus, a complex medium was developed which, when combined with blood plasma of fish in a process, was found to be essential for glochidial transformation to the juvenile stage.